Possibly, but more than likely not. Easy test would be to connect two systems and run simultaneous speed tests on both. If each one maxes out, then yes, you can get more bandwidth this way.

The ONT will assign one IP to the first device that connects. Every other device will look for a DHCP server to get an IP and the ONT will not allow them to get an IP.

You will have one device with and IP and everything else will be stuck.

This is why you have a router. A router has a front end to accept that one IP address and then use its own internal DHCP to allow everything else to access the internet, THROUGH the router. It is a one to many situation. A switch does not have this capability.

The answer is it’s possible, but depends on the ISP.

ONT have a setting similar to cable modems that specify the maximum number of devices that are allowed to be bridged.

Some ISP is only set this for one, some ISPs set this for two, mainly to allow for a customer to swap routers and not have an issue.

The best answer is to try it and see what happens.

You’re not going to break anything.

It shouldn’t lead to additional data it would most likely help distribute the connection to multiple devices

ONT traffic is shared with you and the neighbours but it’s encrypted in transit. The OLT won’t be having any of your shenanigans unless it’s provioned at the ISP side. ( Very unlikely )